Temperature control apparatus



Nov. 27, 1934. c. WILHJELM TEMPERATURE CONTROL APPARATUS Original FiledApril 19, 1 929 2 Sheets-Sheet l w 7 9 a h w. .0 OJ Mm m u w m 0 7 mm 25 M 5 3&3 .AJ 4 6 .J J J 5 r 0 [NVEN T OR.

ATTORW NOV. 27, 1934-. 3 WILHJELM Re; 19,383

TEMPERATURE C ONTROL APPARATUS Original Filed April 19, 1929 2Sheets-Sheet 2 [/VVENTOR.

ATT RNE S.

Reissued Nov. 27, 1934 UNITED STATES PATENT OFFICE 7 TEMPERATURE CONTROLAPPARATUS Original No. 1,829,772, dated'November 3, 1931,

Serial No. 356,379, April 19, 1929.

Application for reissue September 27, 1932, Serial No.

25 Claims.

In the art of regulating the fuel supply to furnaces it has been foundthat many, if not all of the prior art control devices fail to correctlybalance the fuel supply with the fuel demand or requirement in order tomaintain the desired or predetermined operating temperature in thefurnace during changing operating conditions.

So called on and off controls or stepwise operated controls will to someextent maintain a certain temperature, but only accompanied byconstantly recurring fluctuations within a range which is not narrowenough for close control pur: poses.

The object ofthis invention is to provide a temperature controlapparatus including means for correctly balancing the fuel supply withthe fuel demand for a given temperature at varying operating conditionsand whereby, when once the proper adjustment or regulation has beenobtained, further variations will be practically immediately checked andcontrolled.

Further objects ofthe invention and a full understanding thereof will bemore readily obtained from the following specification and explanationread together with the accompanying drawings in which Fig. 1 is ageneral wiring diagram illustrating the invention and Figs. 2 to 4 arediagrammatic illustrations of a certain balancing switch mechanism.

In the drawings the reference numeral 1 denotes a furnace which isheated by fuel supplied through a pipe 2 controlled by a valve 3.

A thermostat of commercial type is mounted in the furnace wall andresponds to temperature changes within the furnace. The thermostat mayconsist of an expansible metal rod 4 which is mechanically connected at5 to a metal tube 6 having a difierent coefiicient of expansion than therod. The tube is fixed in the thermostat frame 7 which is mountedimmovably in any desired manner. The rod is provided with a rack 8 foroperating a gear 9 on the indicator shaft 16 which carries a pointer 11for indicating temperature changes on a scale 12. The indicator shaftalso carries two contact disks l3 and 14 which are adjustably mounted onthe shaft in any well known manner.

- Adjacent the disks 13 and 14 there are mounted two pairs of contacts15, 16 and 1'7, 18 adapted to be closed by means of resilientflngers 19which rest on the disks. 20 is a fixed contact base.

The contacts 15,- 16 and 1'7, 13 control the circuits through two relayswhich comprises a relay coil 21 having a non-conducting armaturecarrying a top and a bottom conducting bar 23 and 24 respectively, and asecond relay coil 25 having a. non-conducting armature alsocarrying atop and bottom conducting bar 26 and 27 respectively.

The armatures are normally in lowered positions as shown, when thebottom bars 24 and 2'? bridge contacts 28, 29 and 30, 31 respectively.When the relay coils are energized the armatures are lifted and the topbars 23 and 26 bridge contacts 32, 33 and 34, 35 respectively.

The numeral 36 denotes a motor which through suitable reducing gearing3'7 drives an interrupter consisting of two cams 38 and 39 mounted onthe shaft 40. The interrupter cams are adapted to close certain circuitsthrough pairs of contacts 41, 42, 43, 44, 45, 46 and open contact 4'7,48 by means of resilient fingers 49 in engagement with the cams. Thecontacts are mounted in fixed bases 50 and 51.

The valve 3 is operated by a link 52 connected to an arm 53 which isslidably pivoted on an adjustable pivot 54. The other end of the arm isconnected at 55 to a link 56 pivoted to a crank disk 57 which is drivenfrom a reversible valve operating motor 58.

The link 56 is connected to a bell crank 59 pivoted on a. stud 60. Onthe latter is also pivoted a switch arm 61 which carries a pin 62.Surrounding the stud there is a spring 160 providing friction betweenthe bell crank 59 and the switch arm 61, see Fig. 4.

The pin 62 is adapted to operate, i. e. oscillate a contactor arm 63pivoted at 64. The arm 63 carries a switch contact 65 on the end of aflexible stem 66. The bell crank 59 and switch arm 61 are ofnon-conducting material, the stem 66 and contact 65 are of conductingmaterial.

On both sides of the switch arms there are mounted conducting contactarms 70, '71 and 72, 73. The contact arms are pivoted in conductingpairs at 74 and 75 respectively. Switch arm 61 operates contact arms 71and 72 to break contacts '77 and '18. Bell crank 59 operates contactarms and '13 to break contacts at 76 and 79.

When the furnace is running at normal, 1. e. the desired operatingtemperature, the parts are in, the position as shown, there is nocurrent passing through the apparatus and the valve will be opened tosome extent, probably half open. When however the temperature changesfor any reason, for instance decreases, the thermostat rod 4 contractsand moves the indicator shaft 10 anticlockwise and the disk 13 closescontacts 15, 16. This establishes several circuits as follows. From theline wire 80 to contacts 15, 16, wire 81 to relay 21 and out to linewire 82. The relay 21 armature is drawn up and contacts 32, 33 areconnected by bar 23 whereby another circuit is made from the line 82through 33, 23, 32 to wire 83, to 77 through contact arms 71 and to thevalve motor 58 and back to the line through wire 84.

A third circuit is made as follows. From the line to relay contacts 33,23, through wire to the interrupter motor 36 and out through wire 86.

The closing of the first circuit referred to en ergizes relay 21. Thedrawing up of the relay armature closes the second circuit through thevalve motor 58 which begins to operate and through the instrumentalitiesreferred to opens the valve a certain distance. At the same time,however, the motor also through the connection 56 operates the bellcrank 59 and switch arm 61 on the stud 60, these two elements 59 and 61moving together because of the friction spring 160. The movement of theswitch arm 61 operates contact arm 71 to break the motor circuit at 77,see Fig. 3, arm 71 being stopped against a fixed stop and also by meansof the pin 64, oscillates the arm 63 whereby contact 65 engages contact78.

It will be observed that the stem 66 is flexed as shown in Fig. 3 due tothe fact that contact 65 engages contact 78 before the oscillatingmovements of the arms 61 and 63 have ceased. The motor is now stoppedand the parts of the switch mechanism are in the position shown in Fig.3 with the bell crank 59 moved nearer towards the contact arm 70.

At this time, therefore, the valve has been opened further in order tofurnish an increased fuel supply in response to the increased fueldemand caused by the lowering of the temperature. The movement of thevalve, however, has necessarily been greater than required in order tomake up for lost time and in order to compensate for the time lag in thefurnace, and the result of the increase in the fuel supply musttherefore be given an opportunity to react on the temperature beforefurther operations of the valve are made.

If the operation of the valve has produced the required increase in thefuel supply and the temperature has been corrected within the time lagperiod of the particular furnace, no further opening movement of thevalve is required and it must now be moved back to a new normalposition, i. e. one in which the fuel supply balances the fuel demandunder the changed conditions in the furnace.

If at this time the valve was merely moved back to its first operatingposition, I would have a simple off and on control and the operationwould obviously not cause the fuel supply to balance the fuel demand.For instance if I assume that before operating the valve a givenquantity of fuel' is required to maintain a temperature of say 560, andthe temperature decreased as aforesaid, it

is obvious that the valve must be moved to a diiferent normal operatingposition in order to 1 supply more fuel to maintain the same temperatureof 500.

Therefore, the terms normal position or'operating position of the valveindicates in this specification a position which at any given timepermits a flow or supply of fuel which balances the fuel demand of thefurnace at that time.

Under ordinary conditions it will be found that the temperature hasresponded to the increased fuel supply. Consequently before the time lagperiod has passed the thermostat rod will commence to expand due to therise in temperature and rotate the disks 13. and 14 clockwise th r ycausing the contacts 15 and 16 to open, the relay 21 will bede-energized,'its armature will fall out and the circuits broken.

At this time it is obvious that if the parts are left undisturbed withthe valve opened to a greater extent than required there will be afurther subsequent rise in the temperature. The valve must therefore beclosed somewhat in order that the fuel supply may balance the changedrequirements of the fuel demand. It is for this reason that we have thecontact 65 in the switch mechanism,

7 because thereby a circuit is made to operate the motor in the oppositedirection as follows.

From the line through wire 87 to contacts 47, 48, which are closed aswill be explained hereafter, to wire 91, through lower relay contacts31, 27, 30, 29, 24, 28, to wire 92, to switch stem 66, contacts 65 and78, arms /72 and 73 to the motor 58 and out. The motor now starts to runin the opposite direction and moves the valve to close it and brings itto a position in which the fuel requirement balances the fuel demand andat the same time, of course, the bell crank 59 has been operated toactuate contact 65 and break the motor circuit at 78 and the motorstops.

Now it will be observed that the valve is not brought back to its formerposition because the second motor circuit by way of the flexed stem andcontact 66, 65 is of shorter duration and the motor has less drift thanfrom the first initial circuit of longer duration through the valvemotor. When the motor starts to run in the direction opposed to itsinitial stroke, the circuit through the motor will last only until thearm 63 has been moved sufliciently to unflex the stem 66. When thishappens the contact 65 will quickly move away from contact 78.. Thismovement is therefore shorter than the first oscillating movement whichcontinues beyond the flexing period until arm 61 operates arm 71, and wenow have the valve in a new normal operating position permitting a fuelsupply which balances the increased fuel demand. This will be morereadily understood when it is remembered that the interruption of theinitial valve moving motor circuit is by separation of arm 71 fromcontact 77 (or 72 from contact 78), while the interruption of theopposite or secondary valve moving motor circuit is by separation of thecontact 65 from contact 78 or 77. The degree of flexing of stem 66 isvariable by'variation of the length of contact 65, as by filing orotheradjustment and the like. One extreme condition may maintain in which thedrifting of the motor after separation of contacts 71 and 77, forexample, will just cause arm 65 to slightly touch contact 78 withoutflexing stem 66, in which case, obviously, the slightest degree ofclosing of the secondary valve moving circuit is immediately terminatedby separation of contacts 65 and 78 (for example) with a consequenteffecting of an extremely small return movement. An alternative extremesituation is one in which the relative length of contact 65 is so greatthat separation of arm 71 from contact 77 is only accomplished afterappreciable motor movement has occurred such as to substantially flexstem 66 whereby the return secondary opposite motor operation would needto be substantially as long in duration as the initial valve closingcircuit. The only requirement for the securing of the mentionedpredeterminedly smaller op- 4 posite canceling movement after a largerinitial valve movement is that the initial normal clearance betweencontact 65 and contact 78 or 77 requires a predetermined duration ofrunning of the motor to close, and which is less than the time of motorrunning required to close the initial clearance between arm 71 andcontact 77, or between arm 72 and contact '78.

If, instead of a decrease in the temperature, an increase occurs, thenthe thermostat rod 4 expands and operates the disks 8 and 14 clockwiseto close contacts 1'7, 18 and relay 25 is energized by way of wire 84and lifts its armature to connect contacts 34, 35. Current then passesto the valve motor by way of the line 82, contacts 34, 26, 35, wire 95to contact '78, to arms 72, 73 to the motor and out.

The valve is then closed somewhat until the motor circuit is broken at'78 by the engagement of arm 61 with arm 72 and the contact 65 is nowmoved to engage contact 77, the parts being in positions the reverse ofthe showing in Fig. 3.

We also at this time have a circuit to the interrupter motor 36 by wayof contact 26 and wire and out as before. Assuming that the closingmovement of the valve is sufllcient to balance the fuel demand withinthe time lag period, then the rod 4 will contract, contacts 1'7, 18 willopen, relay 25 will be deenergized, the armature will drop and all thesaid circuits will be opened.

We also have the same circuit closed as before through the elements 82,87, 47,,48, 91, the lower relay contacts, wire 92 to 66, 65 to 77 and tothe motor to run the latter in the opposite direction to open the valve,that is bringing it back to a new normal operating position subsequentto the rise in the temperature. The switch elements are again operatedand the motor circuit broken at 65, '77.

In the foregoing it has been assumed that the fuel supply has beenregulated to take care of the changed fuel demand on either the plus orthe minus side of the temperature within the time lag period and duringthese operations the valve motor 58 has been operated directly throughthe circuits made at the relays. However, if the valve movement ineither direction has been insufficient, further movements of the valvein the respective directions are caused by way of circuits made throughthe valve motor under the control of the interrupter. The cams 38 and 39will pref erably be set on the shaft 40 in such a manner as to preventclosing of the interrupter controlled circuits within a time lag period,for instance the drawings. show that with the shaft 40 rotatinganti-clockwise, the contacts 41 to- 48 inclusive will remain undisturbeduntil the contact fingers run off the lobes of the cams.

Assume now that the temperature has fallen and that the valve has beenmoved initially as described above, but that the increased fuel supplyis insufficicnt to balance the fuel demand within the time lag period.In such a case it is obvious that one or more additional openingmovements of the valve are required. In other words, further operationsof the valve motor are necessary. Such additional operations are causedby the closing of circuits under the control ofthe interrupter asfollows, it being observed that as soon as relay 21 is energized theinterrupter motor commences to run.

When the lobes of the cams 38 and 39 pass from under the fingers 49contacts 45, 46 are closed to maintain the interrupter motor circuitfrom the line 82, through wire 8'7, contacts 46, 45, wire 85, motor 36and out.

Simultaneously therewith the contacts 41, 42 are also closed and acircuit is made from the relay contact 32, through wire'88, contacts 41,

42, wire 89 to 76 contact arm '70 to the valve motor in the samedirection as the initial circuit and out. Consequently the valve motorreceives a current impulse and runs until the next lobe of the cam 39engages the finger 49 to open the contacts 41, 42 when the motor stops.This additional opening of the valve has increased the fuel supply andmay or may not be sufficient to cause it to balance the fuel demand. Aninspection, of Fig. 3 shows that at this time the bell crank 59 willhave moved closer to the con-- tact arm '70 against the friction at 160.If the additional valve movement has been suflicient, the rise in thetemperature will operate the thermostat rod 4 as above described, relay21 will be de-energized, the circuits will open and the motor will beoperated in the opposite direction via flexible contact member 66, 65 asbefore. The valve will therefore be brought back to a new, third, normaloperating position different from its initial normal position anddifferent from the second normal-position referred to above.

From this it will be seen that in the event the initial movement of themotor 58 and the valve is insuflicient, additional movements occur, onewithin each time lag period, until the fuel supply balances the fueldemand. In the event that correction does not take place before the bellcrank 59, after repeated movements towards the arm '70, engages the arm'70 then such engagement will open the circuit at '76.

The valve will now be fully open and no further movement can occur.This, however, is an extreme case and illustrates the reason for thesecond contact arm '76 in the circuit. It may therefore be said that theswitch mechanism comprises members 71, 72 which upon being operatedbalances the circuit, whereas the members '70, '73 serve more in thenature of an absolute limit switch.

The interrupter also controls the additional movements on the plus sideof the apparatus when the initial valve closing movement occurs by wayof the relay 25. In this case the valve motor58 obtains additionalimpulses through a circuit comprising the line 82, relay contacts 34,26, 35, wires 95, 96, interrupter contacts 43, 44,

wire 97 to contact '72, to arm 73 to the motor invention provides meansfor correctly balancing the fuel supply to the fuel demand by opening orclosing the valve from a normal running position as the case may be andthereafter automatically places the valve in a new normal runningposition to take care of the fuel supply as required by the new demand.That the movements of the valve therefore are corrected within the timelag period within which temperature reaction occurs whereby overshootingthe temperature is prevented and hunting for the correct valve positionis eliminated. Also, that by bringing the valve back to a new normalposition, correction occurs on the same side of the apparatus therebypreventing wide fluctuations. In actual practice this control apparatuswill in most cases provide for a balanced fuel supply by only oneadditional movement of the valve and a chart made from the apparatuswill show little if any variations in temperature unless amatewithin afurnace having a valve controlled fuel supply, a motor for operating thevalve, a main electric circuit, means in the latter for causing themotor to open the valve in response to a decrease in the temperaturewithin the furnace and other means, automatically operated within agiven time interval, for subsequently causing the motor to close thevalve to a lesser extent than the said opening thereof whereby tobalance the fuel supply to the fuel demand required by the said decreasein the temperature. 7

2. In a system for regulating the temperature within a furnace having avalve controlled fuel.

- supply, a motor for operating the valve, a main electric circuit,means in the latter for causing the motor to close the valve in response-to an increase in the temperature within the furnace and other meansautomatically operated within a given time interval, for subsequentlycausing the motor to open the valve to a lesser extent than the saidclosing thereof whereby to balance the fuel supply to the fuel demandvrequired by the said increase in the temperature.

. 3. In a system for regulating the temperature within a furnace havinga valve controlled fuel supply, a motor for operating the valve, anelectric circuit, means in the circuit to cause said motor to operatethe valve in a certain direction in response to a change inthetemperature within the furnace, a switch mechanism in said circuit forsubsequently causing said motor to again operate the valve within apredetermined time interval in the opposite direction to a lesser extentthan the said first operation and means operated by the motor to actuatesaid switch meehanism. v

4. In a system for regulating the temperatu within a furnace having avalve controlled fuel supply, a motor for operating the valve, anelectric circuit, means in said circuit to cause the motor to operatethe valve in a certain direction in response to a change in thetemperature within the furnace, other means in said circuit forsubsequently causing the motor to again operate the valve in the saidcertain direction after a predetennined time interval and to a lesserextent than the said first valve operation if the temperature change isnot corrected and mechanism for causing the motor to operate the valvein a direction opposite to the aforesaid when the temperature returns tonormal.

5. In a system for regulating the temperature within a furnace having avalve controlled fuel supply, a main electric circuit, a motor foroperating the valve, means in said main circuit for causing the motor tooperate the valve in a certain direction in response to a change intemperature within the furnace, a mechanism in said circuit forestablishing a regularly interrupted circuit through the motor to causethe motor to further operate the valve in said certain direction and aswitch mechanism in said circuit for causing the motor to operate thevalve in the opposite direction to a lesser extent than the extent ofthe preceding valve operations.

6. In a system for regulating the temperature within a furnace having avalve controlled fuel supply, a normally open main electric circuit, a

motor for operating the valve, means in said cir- I cuit forautomatically establishing a first circuit for causing the motor tooperate the valve in a certain direction in response to a change intemperature within the furnace, other means in said circuit forestablishing a second regularly interrupted circuit for causing themotor to subsequently operate the valve further in the said certaindirection if the temperature does not return to normal after the firstvalve operation and a switch mechanism in said main circuit forestablishing a circuit for causing the motor to operate the valve in theopposite direction within a given time interval elapsing after the firstoperation of the valve or after any of the subsequent operations thereofwhen the temperature becomes normal. I

'7. In a system for regulating the temperature within a furnace having avalve controlled fuel supply, a normally open main electric circuit, amotor for operating the valve, means in said circuit for automaticallyestablishing a first circuit for causing the motor to operate the valvein a certain direction in response to a change in temperature within thefurnace, other means in said circuit for establishing a second regularlyinterrupted circuit for causing the motor to subsequently operate thevalve further in the said certain direction if the temperature does notreturn to normal after the first valve operation, means in said secondcircuit for interrupting the same for periods equal to the time lagperiod of the furnace, and a switch mechanism in said main circuit forestablishing a circuit for causing the motor to operate the valve in theopposite direction within any time lag period elapsing after the firstoperation of the valve or after any of the subsequent operations thereofwhen the temperature becomes normal.

8. In an automatic valve system, a method of securing a desired valveposition at which fuel demand and fuel supply are substantially balancedwhich consists when furnace conditions change and unbalance of fuelsupply and demand occurs in subjecting the valve to a movement in onedirection to over-correct for such unbalance of demand and supply, andthen in subjecting the valve to another but opposite and predeterminedlysmaller movement to only partially cancel the over-correction toreestabish substantial balance of fuel demand and supply comporting withthe change in furnace conditions.

9. In a systemfor regulating the temperature within a furnace having avalve controlled fuel supply, a motor for operating the valve, a mainelectric circuit, means in the latter for causing the motor to open thevalve in response to a decrease in the temperature within the furnaceand other means automatically operating for subsequently causing themotor to close the valvesuch subsequent movement being always to alesser extent than the said opening thereof whereby to balance the fuelsupply to the fuel demand required by the said decrease in temperature.

10. In a system for regulating the temperature within a furnace having avalve controlled fuel supply, a motor for operating the valve, a main byto balance the fuel supply to the fuel demand required by the saidincrease in temperature.

11. In a system for regulating the temperature within a furnace having avalve controlled fuel supply, a motor for operating the valve, anelectric circuit, means in the latter for subsequently causing the valveto move to vary the flow of fuel in response to a variation intemperature within the furnace, and other means automatically operatingfor causing the motor to move the valve to oppositely vary the flow offuel always to a lesser extent than the first mentioned movement thereofwhereby to balance the fuel supply to the fuel demand required by thesaid variation in temperature.

12. In a control system for furnaces having a valve controlled fuelsupply, means establishing an initial valve setting for the fuel supplyin substantial balance to fuel demands, means for progressivelyyaryingthe substantialy balanced setting of the fuel supply valve in responseto variations in the demands of the furnace, each new balanced settingof the fuel supply valve being always a resultant of an appreciablevariation of the valve setting for the fuel supply and an oppositepartially cancelling variation of the valve setting for the fuel supply.

13. In a system for regulating the temperature within a furnace having avalve controlled fuel supply arranged to establish substantial balancebetween the fuel demands of the furnace and the fuel supply asdetermined by the existence of the furnace temperature within givenlimits, means responsive to variation of furnace temperatures andtherefore to unbalance of fuel demands, means operatively associatedwith the responsive means to vary the fuel supply to an overcorrectingdegree in response to variation in fuel demands, and means automaticallyresponsive to the same fuel demand variation to subsequently change thefuel supply to a predeterminedly smaller opposite degree of variation.

14. In a system .for regulating the temperature within a furnace havinga valve controlled fuel supply arranged to establish substantial balancebetween the fuel demands of the furnace and the fuel supply asdetermined by the existence of the furnace temperature within givenlimits, means responsive to variation of furnace temperatures andtherefore to unbalance of fuel demands, means operatively associatedwith the responsive means to vary the fuel supply to an appreciabledegree to correct for the variation in fuel demand, and meansautomatically responsive to such variation in fuel supply tosubsequently change the fuel supply to a predeterminedly smalleropposite degree of variation to again establish substantial balancebetween fuel demand and fuel supply.

15. In a system for regulating the temperature within a furnace having avalve controlled fuel supply arranged to establish substantial balancebetween the fuel demands of the furnace and the fuel supply asdetermined by the existence of the furnace temperature within givenlimits, means responsive to variation of furnace temperatures andtherefore to unbalance of fuel demands, means operatively associatedwith the responsive means to subject the valve to a plurality ofcontrolling movements to correct for a variation in furnacetemperatures, said movements being always partially cancelling indirection and degree to establish a secondary valve setting ofsubstantialbalance between fuel supply and fuel demand.

16. In a system for regulating the temperature .means to vary the fuelsupply in response to and in degree as a function of variationof suchtemperature to overcorrect for such variation, said means arrangedsequentially automatically oppositely'to vary the fuel supply so asinevitably partially to cancel the first mentioned variation of fuelsupply.

17. In a system for regulating the temperature within a furnace having avalve controlled fuel supply arranged to establish substantial balancebetween the fuel demands of the furnace and the fuel supply asdetermined by the existence of the furnace temperature within givenlimits, means responsive to variation of furnace temperatures andtherefore to unbalance of fuel demands, means operatively associatedwith said responsive means tovary the valve setting of the fuel supplyas a function-of the variation in temperature in the furnace toovercorrect-for the temperature variation, said means arrangedautomatically and predeterminedly only consequently to modify andpartially to cancel the variation in valve setting.

18. In a system for regulating the temperature within a furnace having avalve controlled fuel supply arranged to establish substantial balancebetween the fuel demands of the furnace and the fuel supply asdetermined by the existence of the furnace temperature within givenlimits,. means responsive to variation of furnace temperatures andtherefore to unbalance of fuel demands,

means operatively associated with the responsive.

19. In a system for regulating the tempera-v ture within a furnacehaving a valve controlled fuel supply arranged to establish substantialbalance between the fuel demands of the furnace and the fuel supply asdetermined by the existence of the furnace temperature within givenlimits, means responsive to variation of furnace temperatures andtherefore to unbalance of fuel demands, means operatively associatedwith the responsive means to automatically initiate and consummate acycle of valve controlling operations upon a variation in furnacetemperature, said cycle comprising a primary variation of fuel supplyfollowed inevitably by an opposite partially cancelling secondaryvariation of the fuel supply, said primary variation being in degree afunction of the variation in temperature.

20. In a system for reguating the temperature within a furnace having avalve'controlled fuel supply arranged to establish substantial balancebetween the fuel demands of the furnace and the fuel supply asdetermined by the existence of the furnace temperature within givenlimits, means responsive to variation of furnace temperatures andtherefore to unbalance of fuel demands, means operatively associatedwith the responsive means to automatically initiate and consummate acycle of valve controlling operations upon a prising a primary variationof fuel supply followed inevitably by an opposite partially cancellingsecondary variation of the fuel supply, said primary variation being indegree a function both of the variation in temperature and of a timeinterval.

21. In a system for regulating the temperature within a furnace having avalve controlled fuel supply, means for varying the volume of fuelpassing through the valve a degree dependent upon the extent ofvariation of furnace temperatures from a given range to overcorrect forsame, and means for automatically .predetenninedly partially cancellingsuch volume variation to as tablish a new valve setting pursuant to thefirst mentioned volume variation.

22. In automatic temperature control systems, the method of securingbalance of fuel supply to fuel demands to substantially maintain a givenoperating temperature, which consists in proportioning fuel supply togiven fuel demands to establish an initial setting for the fuel supply,in securing an indication of unbalance of fuel demand, in varying thefuel supply to overcorrect for the unbalance of fuel demand, then duringthe time lag of the furnace securing further indications of fuel demand,and then responsive to the existence of such further indication againvarying the fuel supply toward Greater overcorrection, then finallypartially cancelling the overcorrection to a new normal setting for thefuel supply.

23. The method of securing automatic temperature control in which thefuel supply is substantially balanced against fuel demands of a furnace,which consists in establishing instantaneously substantial balancebetween fuel flow and fuel demands to maintain an operating temperaturewithin a given range with an initial fuel flow setting, in varying thefuel flow in response to unbalance between fuel flow and fuel demand toa degree a function of such unbalance, then in predeterminedlyoppositely varying the fuel flow as a different function of suchunbalance to establish a new fuel flow setting in instantaneoussubstantial balance with fuel demands.

24. In an automatic valve control system, a method of moving a valvefrom an instant position at which unbalance of fuel demand and supplyexists to a desired position at which substantial balance of fuel demandand supply is attained, which consists in subjecting the valve tosuccessive movements in a direction toward and in degree beyond thedesired position as a function of such unbalance, then subjecting thevalve to an opposite movement to return it to the desired positioninevitably spaced from the instant position when the temperature returnssubstantially to a predetermined normal.

25. In an automatic temperature control system, a fuel supply line, avalve in the line,a temperature responsive device having a normalholding range and susceptible to selective deviation on either side ofsaid range and affected by the fuel supply, a motor for operating thevalve, electric circuits controlled by the device, means in the circuitsfor operating the motor to move the valve in a selected direction inresponse to a deviation of the device from theholding range in onedirection to change the fuel supply ultimately to urge the device towardthe holding range, and means automatically operative for causing themotor to move the valve in the opposite direction to a'predeterminedlysmaller degree before the device has deviated from the holding range inits other direction.

- CHRISTIAN WILHJELM.

